1. Field of the Invention
This invention relates generally to content addressable memory (CAM). More particularly, it relates to real-time error detection and/or correction in ternary content addressable memory (TCAM).
2. Description of the Related Art
Content addressable memory (CAM) is a type of memory unit in which the data stored is addressable by its content. During a compare operation, the CAM compares an input word with the words stored in the CAM. The CAM determines whether each entry is a match or a mismatch to the input word. If a match to the input word is found, the CAM may return a list of one or more storage addresses of the entries that matched the input word and/or one or more data words associated with the entries that matched the input word.
A ternary CAM (TCAM) is a type of CAM in which the bits stored in a data entry can have three different values for purposes of matching to the input word (e.g., 1, 0, and X or don't care). Some TCAMs implement the third bit value by adding a mask bit for every bit in the data word, where the mask bit specifies whether the corresponding bit in the data word is an X (i.e., whether a bit in the data entry is a “care” or “don't care”).
Errors may be introduced into entries in a TCAM (e.g., by ionizing radiation). In certain applications, the soft error rates (SER) in TCAMs can exceed acceptable limits for many applications given the large number of bits stored by TCAMs.